Magnetic domain propagation plate with minimized temperature sensitivity

ABSTRACT

WHERE Rho D (1/D) DD/DT d bubble diameter T temperature F magnetostatic force function lambda MATERIAL LENGTH H PLATE THICKNESS So radial stability function Rho 1/ (DO/DT) sigma Ms 1/Ms (dMs/dT) sigma wall energy density per unit area, and Ms saturation magnetization.   A magnetic domain propagation plate having a preferred direction of magnetization normal to the plate and being made of a material and having a plate thickness such that the diameter of bubbles formed in the plate have a minimum sensitivity to temperature variations, these parameters being determined by minimizing the quality Rho d:

United States Patent [191 Torre et al.

[ 51 July 30, 1974 MAGNETIC DOMAIN PROPAGATION PLATE WITH MINIMIZEDTEMPERATURE SENSITIVITY [75] lnventors: Edward Della Torre, Toronto,

Ontario; Magid Dimyan, Hamilton, Ontario, Canada [73] Assignee: CanadianPatents and Development Limited, Ontario, Canada [22] Filed: Oct. 26,1972 [2]] Appl. No.: 300,885

[52] US. Cl. 340/174 TF, 340/174 SC [51] Int. Cl Gllc 11/14 [58] Fieldof Search 340/174 SC, 174 TF [56] References Cited UNlTED STATES PATENTS3,508,22l 4/1970 Thiele 340/174 TF OTHER PUBLlCATlONS lBM Tech Disc.Bulletin, Thermal Manipulation of Bubble Domains" by Gambino et al. Vol.13, No. 7, 12/70, pp. l788-l790. IEEE Transactions on Magnetics,Temperature Dependence of Rare-Earth Orthoferrite Properties Relevant toPropagating Domain Device Applications" by Rossol; Vol. 5, No. 3, 9/69;pp. 562-565.

Primary Examiner-Stanley M. Urynowicz, Jr. Attorney, Agent, or Firm-J.R. Hughes 5 7 ABSTRACT A magnetic domain propagation plate having apreferred direction of magnetization normal to the plate and being madeof a material and having a plate thickness such that the diameter ofbubbles formed in the plate have a minimum sensitivity to temperaturevariations, these parameters being determined by minimizing the qualityp,,:

d bubble diameter T temperature F magnetostatic force function Amaterial length h plate thickness 5,, radial stability function P0 iq 8x K/ owall energy density per unit area, and M, saturationmagnetization.

2 Claims, 3 Draw F gure MAGNETIC DOMAIN PROPAGATION PLATE WITH MINIMIZEDTEMPERATURE SENSITIVITY This invention relates to magnetic domainpropagation plates and more particularly to a method of forming magneticdomain or bubble devices having a fixed bubble diameter insensitive totemperature variations.

In a practical bubble device it is desirable to keep the bubble sizeindependent of temperature in order to keep optimum coupling with driveor propagation circuits.

The temperature sensitivities of bubble diameter in two different typesof uniaxial magnetic materials have been derived in terms of thematerial parameters. See paper entitled Temperature Sensitivity ofBubble Domains by M. Y. Dimyan and E. Della Torre in Journal of AppliedPhysics, Vol. 43, page 1285 (1972).

The temperature coefficient of bubble diameter (p that is the fractionalchange in bubble diameter for a one degree change in temperature, isdefined by Prr (l/d) dd/JT where d is the bubble diameter and T is thetemperature. Similarly, the temperature coefficients of wall energy andthe magnetization (M,) are given by:

The equilibrium equation for bubble diameter is given by:

)t/h (d/h) (H/411-M,) F(d/h) 0 4 where I is the material length definedb )t 0/4'n'M, 5

h is the thickness of the crystal, H is the applied bias field, andF(d/h) is the magnetostatic force function.

Differentiating (4) with respect to temperature under the condition thath and H do not change with temperature yields:

l/h(dI/aT) (d/h)H/41rM, (dM,/([I) /41rM,)l/h(dd/Jf) (dF/dd)dd/a'T 0 (6)From (5) dI/dT l/4'rrM (do'/a l') (20/411'M )dM,/dT 7) or from (2), (3)and (5) d Mp a ZPMS) (8) Now (6) becomes A/h(P PM, /h)( QPM (d/h)([ 3l)Pd 0 (9) where F (d/h)/d(d/h) (10) Eliminating H/41rM, by use of (4)yields (A/h)p a [A/hDPM l )Pd But the radial stability function 5,, isdefined by ow/h) 0/ 1) (d/h) (ll) Therefore It is the object of thepresent invention to provide a method of selecting and forming magneticdomain propagation plates having thickness such that the temperaturecoefficient of bubble diameter is zero or a minimum for bubbles formedin the plate for known operating conditions.

In drawings which illustrate curves on which selection of platethickness may be based:

FIG. I is a plot of the ratio of the fractional changes in wall energydensity and magnetization for zero temperature sensitivity as a functionof plate thickness for two bias conditions,

FIG. 2 is a plot of p /p as a function of thickness for the same twobias conditions, and

FIG. 3 is a plot of optimum thickness normalized to the material lengthas a function of p 0 /p s for two bias conditions d (d,,r1 and d Md, dwhere a, is the bubble collapse diameter and d the run-out diameter.

The following three cases will be considered:

,I. p =0, II. p =O and III. p a O,p 9* O butp 2p Case 1: This applies tomaterials such as mixed rare earth orthoferrites operating near the spinreorientation temperature. Then Pd pa- A plot of p /p a I as a functionof the thickness for this case is shown in FIG. I for two biasconditions, d (d,d and d /(d ,+d where d is the bubble colapse diameter(smallest bubble diameter that can be maintained) and d the run-outdiameter (diameter at which the bubble runs out into a strip). It isseen that for this material the plate should be as thick as possiblesubject to other constraints. Case II; This applies to some garnets attemperature near the compensation temperature. Then Pa PMS Applying (4)this may be rewritten 3 p /p =2 +(d/)\)H/41rM,, (16) Since the secondterm is positive, the condition for p can only be satisfied if P /pM,,-(in FIG. 3 is a plot of optimum thickness normalized to the materiallength as a function of p U lp for the two bias conditions d 01 11 anda' /z(a d where a and d have been defined above. This curve may be usedto select the appropriate uniaxial material which will give zerotemperature sensitivity of bubble diame ter in a bubble device if theoperating conditions are known. Equations (15) and (16) provide means ofdetermining the plate thickness required to give minimum temperaturesensitivity of bubbles provided operating conditions are known and canbe specified.

What is claimed is:

l. A magnetic domain propagation plate having preferred direction ofmagnetization normal to the plate and being made of mixed rare earthorthoferrite material and having a plate thickness such that thediameter of bubbles formed in the plate have a minimum sensitivity totemperature variations, said thickness being determined by minimizingthe quantity p F is the magnetostatic force function A is the materialcharacteristic length h is the plate thickness S is the radial stabilityfunction p (1/o-)dcr/Jl" O (for rare earth orthoferrite) h M h where Fis the magnetostatic force function A is the material characteristiclength h is the plate thickness S is the radial stability function p a(1/a)d(r/dT p (1/M,)d ,/dT 0 (for garnet materials) a is the wall energydensity per unit area M is the saturation magnetization, and

T is the temperature.

1. A magnetic domain propagation plate having preferred direction ofmagnetization normal to the plate and being made of mixed rare earthorthoferrite material and having a plate thickness such that thediameter of bubbles formed in the plate have a minimum sensitivity totemperature variations, said thickness being determined by minimizingthe quantity Rho d 1/d(dd/dT):
 2. A magnetic domain propagation platehaving preferred direction of magnetization normal to the plate andbeing made of garnet material and having a plate thickness such that thediameter of bubbles formed in the plate have a minimum sensitivity totemperature variations, said thickness being determined by minimizingthe quantity Rho d 1/d(dd/dT):